Referring to FIG. 1, a conventional lamp device 11 for a heavy duty vehicle 12, such as a truck, a trailer, etc., is mounted on a mounting area 121 in a left or right side of a head of the vehicle 12, and includes a lamp housing unit 110 which is disposed on the mounting area 121 and which defines two separate mounting areas 101 to respectively accommodate a headlight 111 and a first turning lamp 112, and a second turning lamp 113 which is disposed on an outer side of the vehicle 12 and which is put on with the first turning lamp 113 for indicating a turning operation to other vehicles, such as vehicles at the side. Since the headlight 111 and the first turning lamp 112 are respectively mounted in the separate mounting areas 101, light emitted from the headlight 111 and the first turning lamp 112 is limited in the individual areas 101 with limited lighting range thereof. Moreover, it is required to dispose the additional second turning lamps 113 to the heavy duty vehicle at two sides, which results in high manufacturing and replacing cost.